Ferrite power limiter duplexer



y 1965 J. CARTER ETAL FERRITE POWER LIMITER DUPLEXER Filed April 18, 1960 TO SIGNAL RECEIVER TO DUMMY LOAD DC MAGNETIC FIELD I-V FIG. I

FIG. 2

RECEIVE CONDITION I TO RECEIVER TO DUMMY LOAD ANTENNA TRANSMITTER ANTENNA TRANSMIT CONDITION 0c MAGNETIC Fla, 5

INVENTORS, JOHN L. CARTER IRVING REINGOLD.

A T TOR/VEX United States Patent 3,183,457 FERPJTE POWER LilvfiTER DUPLEXER John L. Carter, Asbury Park, and Irving Reingold, Deal Park, Deal, N..l., assignors to the United States of America as represented by the Secretary of the Army Filed Apr. 18, 1%0, Ser. No. 23,1ti6 4 Qlaims. (Cl. 333-10) (Granted under Title 35, US. Code (1952), see. 266) The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment of any royalty thereon.

This invention relates to electromagnetic wave transmission systems and more particularly to microwave duplexing systems employing a ferrite element.

Heretofore, the non-linear attenuation characteristics of gyromagnetic elements such as .ferri-tes were utilized to detune a waveguide cavity to form a transmit-receive switch for duplexing circuits. However, since the detuning resulted from a change in absorption of power in the ferrite, such systems were found to be limited in operation for comparatively low power levels.

It is a principal object of the present invention to provide an improved low loss duplexing device capable of operation for relatively high power levels.

It is another object of the present invention to provide separate paths of power flow in a microwave transmission system by means of a power limiter comprised of a gyromagnetic switching element.

It is another object of the present invention to provide an improved microwave duplexer which requires no gasfilled or other electronic discharge tubes which are limited in life and power rating because of arc loss.

In accordance with the present invention there is provided a micro-wave duplexer which includes a center dual waveguide portion comprising two waveguide sections having a narrow-wall in common and a first and second short-slot hybrid coupler respectively terminating each end of the center dual waveguide portion. Also included are a first and second ferrite slab respectively afiixed to a corresponding wide wall of each of the waveguide sections comprising the center dual Waveguide portion. Included further is a direct-current magnetic field applied to the center dual waveguide portion in a direction parallel to the broad dimension of the wide walls thereof. The ferrite slabs are equally spaced from the narrow common wall, or from the opposed narrow walls, and extend the same distance longitudinally within their respective waveguide sections.

For a better understanding of the invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawings in which:

FIG. 1 shows a perspective exploded view of one embodiment of a balanced microwave duplexer in accordance with the invention;

FIGS. 2 and 3 respectively show diagrams used to illustrate the operation of the microwave duplexer of the invention in the signal receiving and signal transmitting conditions; and

FIGS. 4 and 5 illustrate in perspective, partially cutaway, other embodiments of the invention.

Referring now to FIG. 1 of the drawing, the duplexer shown therein comprises a center waveguide section 19 intermediate two similarly constructed end waveguide sections 12 and 14. The center section 10 comprises two like adjoining rectangular waveguides 15 and 16 having one narrow wall 18 in common. Afiixed to one wide wall of waveguide 15 and slightly spaced from narrow wall 18 is a slab '20 of ferrite material which extends within the interior of guide 15 in a direction parallel to its longitudinal axis. It has ben found that the spacing of the ferrite slab 20 from narrow wall :18 may extend up to 0.200 inch, with optimum spacing at 0.050 inch. Similarly, atfixed to a corresponding wide wall of waveguide 16 is a slab 22 of ferrite material which is spaced the same distance from narrow wall 18 as that of slab 20 in waveguide 15 and extends within the interior of guide 16 in a direction parallel to its longitudinal axis. The lengths of both ferrite slabs are identical. It is to be understood of course that both slabs are made from the same ferromagnetic material, for example, polycrystalline ferrite material, appropriate to the operating frequency range of the microwave signals to be propagated over the guide when the duplexer is in use. The longitudinal dimension of the ferrites determines the center frequency permitted to pass through waveguides 15 and 16. While the cross-sectional dimensions :of ferrite slabs 29 and 22 are not critical, for optimum operation in the X-band frequency range it was found to be 0.15 x 0.200" with the length of the ferrites being approximately one inch. As indicated by the arrow, ia direct-current magnetic field is applied parallel to the broad dimension of the waveguides 15 and 16. The field strength was not found to 'be critical for X-band frequency operation since for this frequency range it was found that the strength of the magnetic field could be varied between 600 and 1200 oersteds for optimum operation.

Each of the end waveguide sections '12 and '14 comprise an identical directional coupler which is a conventional broad band short-slot hybrid junction of the quadrature type such as illustrated and described in the article entitled The Short-Slot Hybrid Junction, by Henry J. Riblet, in the February 1952 issue of the Proceedings of the IRE (pages -184), vol. 40. As shown in FIG. 1 each of these couplers comprises two rectangular waveguide sections 2 and 26 having the same cross-sectional dimensions as the center waveguide sections 15 and 16. The waveguide sections 24 and '26 have one narrow wall in common which is provided with a centrally located longitudinaly-extending slot 28 providing coupling between the two guides. The width and length of slot 28 controls the degree of coupling between the two guides 24 and 26 and is arranged to provide a coupling ratio of 3 db. As explained in the above mentioned article, when signal power is incident on one of its two waveguides, 24 and 26, at terminal 1 it proceeds along this guide until it encounters the coupling slot which divides the signal energy between the two wave-guides 24 and 26 so that the energy leaving terminal ll of one guide just equals that leaving at terminal 12 of the other guide. The network described above including the center waveguide section 10 and end waveguide 3 db short-slot hybrid couplers 1'2 and 1'4 is connected at its terminals to a microwave radar or similar two-way radio system to form a balanced duplexer. As shown in FIG. 1, the terminal 1 of hybrid coupler 12 is connected to the microwave transmitter or other source of radio frequency signal power; the terminal =2 of hybrid coupler 12 is connected to a common transmitting and receiving antenna; the terminal '1 of hybrid coupler 14- is (a connected to a signal receiver; and terminal 2 of hybrid coupler 14 is connected to a non-reflective termination or dummy load.

The operation of the balanced duplexer of the invention as shown in FIG. 1 will be described in connection with the diagram of FIGS. 2 and 3 which indicate by the arrowed straight and curved lines the distribution of the signal energy produced by the duplexer in the signal receiving and signal transmitting condition, respectively, of the associated radar system. The operation of the system is based upon the fact that the propagation constant through the ferrite is non-linear as a function of incident power. This principle of operation is well known and is described in an article by H. Suhl for Non-Linear Behavior of Ferrites at High Microwave Power Levels, pages 1270-1284 in the October 1956 issue of the Proceedings of the IRE. At high power levels, the center waveguide section acts like a waveguide beyond cut-off and essentially all energy is reflected from this section. That is, once the D.-C. magnetic field parallel to the broad dimension of the waveguides and 16 is adjusted for the operating frequency desired, then the insertion loss of the center waveguide section 1! will be high for the incident RF transmitted power to effectively provide a reactive insertion loss circuit. However, with the same applied D.-C. magnetic field at low incident received power the center waveguide section 10 will provide very little attenuation or low insertion loss. Thus, the insertion loss is a direct function of the incident RF power and operates on the RF magnetic field excitation of spin waves in the ferrites rather than the D.-C. magnetic field which is continuously applied. The sequence of events during transmission is illustrated in FIG. 3. The high power transmitter energy applied to input terminal 1 of waveguide 24 of hybrid coupler 12 will be split at the slot 28 into two equal energy portions one of which passes straight through the guide 24 to the output terminal 1 and the other of which will cross over to the guide 26 and pass through to the output terminal 2 As indicated at the left in FIG. 3, the voltage crossing over leads the voltage passing through by 90. The reflected energy from both center waveguides 15 and 16 will again be divided at the slot 28 into two equal energy portions. One of the two portions of this reflected energy will pass directly through the waveguide section 24 or 26 in which it originated, to the asso ciated input terminal, and the other will cross over to the other waveguide 24 or 26 and will pass thereover to the input terminal of coupler 12 associated with that waveguide section. As indicated by the arrowed lines at the left of the diagram of FIG. 3, the relative phases of the reflected energy portions are such that the two energy portions delivered to the transmitter arm are opposed and balance out and the two energy portions delivered to the antenna arm reinforce each other. The reinforced transmitted energy represents all of the transmitted signal power which is channeled to the associated antenna for radiation thereby.

For received signals at low power levels, energy incident on the antenna will be applied to waveguide section 26 of hybrid coupler 12 at its input terminal 2 and will be propagated therethrough to the coupling slot 28 where it will be divided into two equal energy portions. As illustrated at the left of the diagram of FIG. 2, one :of these energy portions will pass straight through waveguide 26 to its output terminal 2 and the other portion, lagging the first portion by 90 will cross over to the waveguide 24. through slot 28 and pass therethrough to the output terminal 1 Since the power in waveguide 24 and 26 is relatively low, the propagation constant of the ferrites in center section 10 is such that energy is transmitted therethrough with essentially no loss. Thus, at the 3 db coupler section 14, each of the applied signal energy portions will be divided into two equal energy portions having the relative phase relationships shown in FIG. 2. One energy portion will pass directly to the same waveguide to which it is applied to its output terminal. The other energy portion will pass through the coupling slot and cross over to the other waveguide and pass therethrough to its output'terminal. The relative phase relations between the two signal energy portions appearing at each of the two output terminals of hybrid coupler 14 are such that they will add vectorially to balance out at terminal 2 connected to the dummy load, and will reinforce each other at terminal 1 connected to the signal receiver. The resulting reinforced received signal will be detected in the signal receiver.

FIG. 4 illustrates another embodiment of the center ferrite limiter waveguide section 10. In FIG. 4, where like numerals refer to like components, the ferrite slabs 20 and 22 are shown as being affixed to corresponding wide walls of respective waveguides 15 and 16 as in FIG.

I, but are equally spaced from their respective opposing narrow side wall instead of the common center wall 18. In this case, however, the magnetic field applied in a direction parallel to the wide walls of center portion 10 would be reversed as indicated by the arrow shown in FIG. 4. It has also been found that the center section 10 operates in the desired fashion when similar ferrite slabs are arranged in opposition .to the two ferrite slabs :shown in FIG. 4. Such an arrangement is shown in FIG. 5, wherein the top and bottom ferrites in each of the center waveguide sections are symmetrically positioned relative to each other. Experiments have shown that the systems shown in FIGS. 1 and 5 provide a duplexer which is relatively broad banded, 67% bandwidth having been achieved.

While there has been described what is at present considered to be the preferred embodiment of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is therefore aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A microwave duplexer comprising a center dual waveguide portion including two waveguide sections having a narrow common wall, a first and second short-slot hybrid coupler respectively terminating each end of said center dual waveguide portion, a first and second ferrite slab respectively aflixed to a cor-responding wide wall of each of the waveguide sections comprising said center dual waveguide portion and spaced from the oppositely disposed wide walls thereof, said ferrite slabs being equally spaced from said narrow common wall and extending the same distance longitudinally within their respective waveguide sections, and a direct-current magnetic field contlnuously applied to said center dual waveguide portion in a direction parallel to the broad dimension of the wide walls of said center dual waveguide portion, said ferrite slabs being adapted to refiect relatively high power energy and being pervious to relatively low power energy.

2. A microwave duplexer comprising a center dual waveguide portion including two waveguide sections having a narrow common .Wall, a first and second ferrite slab respectively affixed to a corresponding wide wall of each of the waveguide sections comprising said center dual waveguide portion and spaced from the oppositely disposed wide walls thereof, said ferrite slabs being equally spaced from opposing narrow walls of said center dual waveguide portion and extending longitudinally within their respective waveguide sections, a direct-current magnetic field continuously applied to said center dual waveguide portion in a direction parallel to the broad dimension of the wide walls of said center dualwaveguide portion, said ferrite slabs being adapted to reflect relatively. high power energy and being pervious to relatively low power energy, and a first and second short-slot hybrid coupler respectively terminating each end of said center dual waveguide portion.

3. The microwave duplexer as set forth in claim 2 and further including a third and fourth ferrite slab respectively positioned opposite said first and second ferrite slab in symmetrical arrangement thereto.

4. The microwave duplexer in accordance with claim 1 wherein the spacing between the ferrite slabs and said narrow common Wall is 0.050 inch.

References Cited by the Examiner UNITED STATES PATENTS 2,586,993 2/52 Riblet 33313 X 6 2,920,292 1/60 Scovil et al 333 13 x 3,011,134 11/61 Reingold 333-4 3,058,070 10/62 Reingold et al 333-11 5 1 OTHER REFERENCES Modern Advances in Microwave Techniques, J. Fox, ed., Brooklyn Poly. Inst., July 1955, pages 221-224 relied on. v

19 HERMAN KARL SAALBACH, Primary Examiner.

FREDERICK M. STRADER, Examiner. 

1. A MICROWAVE DUPLEXER COMPRISING A CENTER DUAL WAVEGUIDE PORTION INCLUDING TWO WAVEGUIDE SECTIONS HAVING A NARROW COMMON WALL, A FIRST AND SECOND SHORT-SLOT HYBRID COUPLER RESPECTIVELY TERMINATING EACH END OF SAID CENTER DUAL WAVEGUIDE PORTION, A FIRST AND SECOND FERRITE SLAB RESPECTIVELY AFFIXED TO A CORRESPONDING SAID CENTER EACH OF THE WAVEGUIDE SECTIONS COMPRISING SAID CENTER DUAL WAVEGUIDE PORTION AND SPACED FROM THE OPPOSITELY DISPOSED WIDE WALLS THEREOF, SAID FERRITE SLABS BEING EQUALLY SPACED FROM SAID NARROW COMMON WALL AND EXTENDNG THE SAME DISTANCE LONGITUDINALLY WITHIN THEIR RESPECTIVE WAVEGUIDE SECTIONS, AND A DIRECT-CURRENT MAGNETIC FIELD CONTINUOUSLY APPLIED TO SAID CENTER DUAL WAVEGUIDE PORTION IN A DIRECTION PARALLEL TO THE BROAD DIMENSION OF THE WIDE WALLS OF SAID CENTER DUAL WAVEGUIDE PORTION, SAID FERRITE SLABS BEING ADAPTED WAVEGUIDE PORTION, SAID FERRITE AND BEING PREVIOUS TO RELATIVELY LOW POWER ENERGY. 